This invention relates to an antenna configuration which includes a dipole ring array for a circularly polarized shaped pattern.
Circularly polarized omnidirectional antennas with dipole arrays are known, for example for FM and TV broadcasting. U.S. Pat. No. 2,518,933 to Redheffer discloses an antenna for radiating circularly polarized waves having a fibrous material arranged in a spiral. U.S. Pat. No. 2,631,237 to Sichak et al teaches an antenna for producing circularly polarized waves comprising a first set of a plurality of coplanar elements and a second set of elements perpendicular to the first set. U.S. Pat. No. 2,639,382 to Jarvis shows an antenna including an element having a number of dipoles extending from a transmission line. U.S. Pat. No. 3,348,228 to Melancon discloses a tri-dipole antenna having a circular disc with half of each dipole on each side of the disc. U.S. Pat. No. 3,427,622 to Kandoian et al teaches a loop antenna comprising at least one loop and radially connected spokes and a central feed. U.S. Pat. No. 3,487,414 to Booker shows an omnidirectional antenna including a pair of discs with two semiannular pieces of metal foil mounted on the first disc and a plurality of radially projecting rods carried in the second disc. U.S. Pat. No. 4,083,051 to Woodward discloses a circularly-polarized antenna having a plurality of dipoles spaced in a circle about a metal mast, the dipoles being titled at an angle with respect to the plane of the circle, and the dipoles being fed in phase rotation with adjacent dipoles 90 degrees out of phase. U.S. Pat. No. 4,297,711 to Ekstrom teaches an omnidirectional antenna comprising at least one circular element including a circular metal plate with a slot and metal band. U.S. Pat. No. 4,315,264 to Du Hamel shows a circularly polarized antenna with circular arrays of slanted dipoles mounted around a conductive mast, the lengths and angles of the dipoles being adjusted for providing circularly polarized radiation.
Some satellite communication antennas require a pattern null near the axis and high gain to the sides with circular polarization and minimum losses. One example is a global positioning navigation system having several satellites and using an integrated transfer system (ITS) for data communication between satellites. A center null is desirable in the pattern to avoid potential interference from the earth. A ring array of circularly polarized elements will have the desired characteristics, but circularly polarized elements require a lot of space and have higher losses than linearly polarized elements. One prior approach to this problem, proposed by Ford Aerospace Corporation, is called a coaxial cavity resonator. This cavity radiates linear polarization, relying on phasing of the ring to suppress cross polarization.